Brake Master Cylinder: Description and Operation

LEGEND
1. Secondary plunger
2. Secondary spring
3. Recuperation seal - secondary
4. Primary spring
5. Recuperation seal - primary
6. Primary plunger

OVERVIEW
A tandem master cylinder, which is assisted by a lightweight compact servo, is fed by a divided fluid reservoir. The rear section supplies fluid for the primary circuit and the front section the secondary circuit.

OPERATION
When the brakes are off, the fluid can move unrestricted between the dual line system and the separate reservoirs in the fluid supply tank. When the footbrake is applied, the primary plunger assembly moves up the cylinder bore and the pressure created acts in conjunction with the primary spring to overcome the secondary springs, thus moving the secondary plunger assembly up the bore at the same time. Initial movement of both plungers takes the recuperating seals past the cut-oft holes in the cylinder chambers (A) and (C), and applies pressure to the fluid in those chambers, which is directed to the respective cylinders of each of the separate circuits.

The fluid in chambers (B) and (D) is unaffected by movement of the plungers and can move unrestricted between the separate chambers and respective reservoirs in the fluid supply tank, both before and during brake application. When the brakes are released, the plunger assemblies, aided by the return springs are retracted faster than the fluid; this creates a depression between the fluid in chambers (A) and (C) and the recuperation seals.

The recuperation seals momentarily collapse, allowing fluid in chambers (B) and (D), which is unaffected by the movement of the plungers, to flow through the holes in the plungers, over the collapsed seals and into chambers (A) and (C) respectively. The movement of fluid from one set of chambers to the other, is compensated for by fluid from the separate reservoirs in the supply tank moving through the feed holes in the cylinder. Conversely, the final return movement of the plunger assemblies causes the extra fluid in chambers (A) and (C) to move through the cutoff holes into the fluid reservoir.